An idealized LC filtering circuit is shown in FIG. 1, and a schematic diagram of an equivalent circuit of the LC filtering circuit in the practical application (particularly in the microwave domain) is shown in FIG. 2. In the practical application, an inductor L is equivalent to an idealized inductor LCM connected in parallel with a parasitic resistor (an equivalent parallel resistor EPR) and a parasitic capacitor (an equivalent parallel capacitor EPC), and a capacitor C is equivalent to an idealized capacitor Cy connected in serial with a parasitic inductor (an equivalent series inductor ESL/2) and a parasitic resistor (an equivalent series resistor EPR/2).
Further, as shown in FIG. 3, a conductor has similar characteristics to the above description in a high-frequency domain. In FIG. 3, an actual wire is shown on the left side, and two equivalent models of the wire in the high-frequency domain are shown on the right side.
A parasitic inductance and a parasitic capacitance of the conductor such as the inductor and the capacitor may influence the insertion loss and EMI (electromagnetic interference) of the circuit. FIG. 4 shows a graph of a simulation result of the circuit shown in FIG. 1. Referring to FIG. 4, a curve 1 represents the insertion loss of a filter constructed with ideal elements, a curve 2 represents the insertion loss in the case where only the series parasitic inductance is taken into account, a curve 3 represents the insertion loss in the case where the parallel parasitic resistance and the series parasitic resistance are taken into account, a curve 4 represents the insertion loss in the case where the parallel parasitic capacitance is taken into account, and a curve 5 represents the insertion loss in the case where the above four parasitic parameters are taken into account.